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Both zinc ore Sphalerite and calcium plagioclase feldspar Anorthite have perfect cleavage that will split cleanly if you hit them with a hammer, but only one can claim a larger split of your votes!
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Cronstedtite from
State Route 9 rock cuts, Haddam, Middlesex County, Connecticut, USA


Classification
Species:Cronstedtite
Formula:Fe22+Fe3+((Si,Fe3+)2O5)(OH)4
Comments:A drab greenish-brown to almost black mineral, abundantly associated with grunerite, siderite, and marcasite, was identified as chamosite. Careful restudy of X-ray data indicates cronstedtite as a better fit.
Habit:radial groups of flattened crystals
Colour:greenish-brown to almost black
Quality for species:Poor for species, only of interest for locality collectors. (#)
Confirmation
Validity:Believed Valid
Data
Mineral Data:Click here to view Cronstedtite data
Locality Data:Click here to view State Route 9 rock cuts, Haddam, Middlesex County, Connecticut, USA
Data Identifiers
Mindat Occurrence Record ID:920671
Long-form Identifier:1:3:920671:7
GUID (UUID V4):0
Nearest other occurrences of Cronstedtite
61.5km (38.2 miles) ⓘOld Mine Park (Old Tungsten Mine), Long Hill, Trumbull, Fairfield County, Connecticut, USA
References
Schooner, Richard. (circa 1985), Untitled manuscript on central Connecticut mineralogy.
 
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